A print head, e.g. an inkjet print head, includes a reservoir holding the printing material, e.g. liquid ink. The print head further includes a plurality of nozzles being in fluid communication with the reservoir. The nozzles are provided at a surface of the print head and allow expelling the print material held in the reservoir onto a recording medium, e.g. a sheet of paper. During a print operation the print head and the recording medium move relative to each other for generating a desired print out, e.g. an image or text, on the recording medium by expelling the print material from the reservoir via the nozzles onto the recording medium.
When the printer including such a print head is inoperative the nozzles are not used. Leaving the nozzles in such an operating state unprotected may cause an interaction between the print material in the reservoir and the environment which may have a detrimental effect on the printing material, e.g. an ink, held in the reservoir. This interaction may cause a vapor transmission from the print material via the nozzles. In addition, the nozzles may be effected, e.g. by clogging due to dried print material particles.
To avoid such detrimental effects a printer is provided with a capping system that includes an elastomeric or flexible cap held by a support element. The cap can be brought into engagement with the print head to form a seal around the nozzles. Providing a cap on the print head in an idle state of the print head extends the life time and the reliability of the print head. To reliably seal the nozzles the cap is in a continuous engagement with a surface of the print head on which the nozzles are arranged so that leaks are avoided.
However, print heads and/or the cap support element may not be manufactured perfectly. The print head surface and/or the cap support element may not be perfectly straight, e.g. the print head surface and for the cap support element may have a curvature. The print head may have two ends along a dimension that are recessed when compared to a center part. In another case the center part of the print head may be recessed when compared to the ends along a dimension of the print head. This results in a bow or a curvature in the print head surface that needs to be compensated for by the elastomeric cap yielding a specific degree of compliance. However, such compliance of the cap material is finite. In case the bow or curvature becomes excessive, despite the compliance of the cap material a complete seal around the nozzles may no longer be achieved. In case the center part of the print head is recessed a leak in the seal at this part may occur as the cap rests tightly on the opposed ends of the print head and is compressed there, however, the compliance of the material is not sufficient to also allow for a tight seal at the central part of the print surface. This reduces the effects achievable by providing the cap around nozzles of a print head.
This problem may be encountered in any kind of print head, however, the larger the dimension of a print head and the larger the dimension of the cap for sealing the print head become, the more severe this problem becomes as manufacturing such elements in accordance with the desired tolerances becomes more difficult. For example, in a page width printer a print head or print bar is used that extends over the print area, e.g. over the width of a page to be printed. Such a print bar and the associated capping system may be made from long parts made of plastic and/or metal that are difficult to manufacture perfectly straight so that these parts may have a curvature which may not be compensated for by the elastomeric cap material so that the above mentioned leak in the seal may occur.